Alkylation catalyst and processes for preparing

ABSTRACT

A composition useful for catalyzing alkylation and transalkylation reactions comprises a molecular sieve having alkylation and/or transalkylation activity, an inorganic refractory oxide component and greater than about 250 ppmw ammonium ions, calculated as (NH 4 ) 2  O on a volatiles-free basis. Such a catalyst has been found to be highly selective for the production of cumene in an intergrated process in which benzene is alkylated with propylene and transalkylated with diisopropylbenzene. The catalyst can also be used to selectively produce ethylbenzene via an intergrated process in which benzene is alkylated with ethylene and transalkylated with diethylbenzene.

BACKGROUND OF THE INVENTION

This invention relates to alkylation and transalkylation processes and acatalyst for use therein. The invention is particularly concerned with acatalyst which, when used in alkylation and transalkylation processes,minimizes side reactions, such as cracking and cyclization, that lead toundesired by-products and therefore has an improved selectivity for thedesired product.

In the past it has been common practice to alkylate aromatic moleculessuch as benzene, toluene and xylene with ethylene, propylene and otherolefins using acidic homogeneous Friedel-Crafts type catalysts such asaluminum halides or heterogeneous acidic silica-alumina catalysts. Suchprocesses have several disadvantages including corrosion problems causedby some of the catalysts and difficulty in controlling the productdistribution obtained from the alkylation reactions. Often, the desiredproduct is the monoalkylate rather than the di- or trialkylate. In aneffort to avoid a large production of di- and trialkylate products andto extend catalyst life, it is conventional practice to use a largeexcess of the aromatic compound.

To avoid some of the problems associated with earlier commercialalkylation processes, solid zeolite-containing catalysts have been usedin recent years to promote the alkylation of aromatic compounds witholefins and other alkylating agents, especially the alkylation ofbenzene with ethylene. Such zeolite-containing catalysts are normallyprepared by combining a zeolite with a refractory oxide binder orprecursor thereof, mulling and extruding the mixture, drying theextrudates and then calcining the dried extrudates at high temperaturesto provide the extrudates with the strength required to withstandcommercial operations. Naturally occurring and synthetic zeolitestypically contain a relatively large concentration of sodium ions andare therefore not catalytically active. Thus, before a zeolite is mixedwith the refractory oxide component or precursor thereof in themanufacturing of a zeolite-based catalyst, the zeolite is normallysubjected to ion exchange, typically with ammonium ions, to reduce itssodium concentration as low as practically possible and increase itscatalystic activity. However, since ammonia is known to poison the acidsites of the zeolite, it is common practice to carry out the calcinationof the dried extrudates at such temperatures that substantially all ofthe ammonium ions in the catalyst are decomposed into hydrogen ions andammonia which is driven out of the catalyst as a gas. Often, suchcatalysts will contain less than 50 ppmw ammonium ions, calculated as(NH₄)₂ O on a volatiles-free basis.

Normally, zeolite-based alkylation catalysts prepared as described aboveare used in fixed bed reactors through which the reactants arecontinuously passed. Although such fixed bed processes usingzeolite-containing catalysts have advantages over earlier commercialprocesses, the selectivity for monoalkylation, especially when producingcumene by reacting propylene with benzene, has been observed in pilotplant studies to vary from one catalyst batch to another with some ofthe selectivities being so low that impurities appear in the productstream in concentrations large enough to dictate the use of additionalequipment or process modifications to reduce the impurity level.

Accordingly, it is one of the objects of the present invention toprovide a catalyst containing a zeolitic or nonzeolitic molecular sieve,and a method for preparing such a catalyst, that has high selectivitiesfor the desired product when used to catalyze alkylation andtransalkylation reactions, which selectivities do not substantially varyfrom one batch of catalyst to another. This and other objects of theinvention will become more apparent in view of the following descriptionof the invention.

SUMMARY OF THE INVENTION

In accordance with the invention, it has now been surprisingly foundthat the selectivity of catalysts comprising an inorganic refractoryoxide component and a crystalline molecular sieve is sensitive to theammonium ion concentration in the catalyst. It has been further found,contrary to what is commonly believed in the art, that it is mostdesirable to maintain a minimum concentration of ammonium ions in suchcatalysts in order to avoid the production of undesirable amounts ofby-products during alkylation and transalkylation. It has been foundthat this minimum concentration is about 250 ppmw ammonium ions,calculated as (NH₄)₂ O on a volatiles-free basis, preferably about 500ppmw, and can range to an upper limit of about 20,000 ppmw. Accordingly,the invention is directed to a catalyst composition of stable and highselectivity which, in its broadest embodiment, contains a molecularsieve and at least about 250 ppmw ammonium ions, calculated as (NH₄)₂ Oon a volatiles-free basis. Preferably, the molecular sieve used inpreparing the catalyst is a steam-stabilized, modified Y zeolite. Theconcentration of ammonium ions in the catalyst typically ranges betweenabout 1000 and 18,000 ppmw, calculated as (NH₄)₂ O on a volatiles-freebasis, preferably between about 2000 and about 15,000 ppmw, morepreferably between about 3000 and about 10,000 ppmw, and most preferablybetween about 4000 and 8000 ppmw. All concentrations referred to hereinas being calculated on a volatiles-free basis are calculated based onthe weight of the catalyst after it has been heated in an oven at 1000°C. for 2 hours to drive off moisture and other volatiles.

The catalyst of the invention is typically prepared by exchanging amolecular sieve with ammonium ions, mixing the resultant ion-exchangedsieve with a porous, inorganic refractory oxide component or precursorthereof, extruding the resultant mixture to form extrudates, drying theextrudates and then calcining the dried extrudates under conditions tocontrol the amount of ammonium ions that are decomposed into ammonia andhydrogen ions so that the ammonium ion concentration of the catalyst isabove the minimum level of 250 ppmw. As used herein, "extruding"includes all forms of pelleting including tableting, extruding, prillingand the like. Alternatively, if it is desired to use the catalyst in afluidized bed reactor, a slurry of the ammonium-exchanged molecularsieve and refractory oxide component can be prepared and subsequentlyspray-dried to produce particles which typically range between 40 and 80microns in diameter and have the desired ammonium ion concentration.

Catalysts of the invention have been found to have consistently highselectivities for the desired alkylated products and are thereforeuseful in a variety of alkylation and transalkylation processes in whichan organic feedstock is contacted with an organic reactant to form analkylated organic compound in the presence of such catalysts. In onespecific embodiment of the process of the invention, the catalyst of theinvention is employed in the alkylation zone of a process for producingcumene (isopropylbenzene) via the alkylation of benzene with propyleneand is also employed downstream in the process in a transalkylation zonewherein benzene is subjected to transalkylation by contacting it withdiisopropylbenzene, an undesired by-product of the reaction betweenbenzene and propylene, to produce additional quantities of cumene.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 in the drawing is a schematic flow diagram of a process forproducing cumene or ethylbenzene utilizing both alkylation andtransalkylation reactors containing the catalyst of the invention;

FIG. 2 is a plot which shows the concentration of undesirableethylbenzene in the product resulting from the transalkylation ofbenzene with diisopropylbenzene to produce cumene versus the conversionof diisopropylbenzene at various concentrations of ammonium ions in thecatalyst; and

FIG. 3 is a plot derived from FIG. 2 which shows the concentration ofundesirable ethylbenzene in the product resulting from thetransalkylation of benzene with diisopropylbenzene to produce cumeneversus the ammonium ion concentration in the catalyst atdiisopropylbenzene conversions of 55, 65 and 75 percent.

DETAILED DESCRIPTION OF THE INVENTION

The molecular sieve-containing catalyst of the invention, which istypically free of hydrogenation metal components, will normally comprisea zeolitic or nonzeolitic molecular sieve composited with a porous,inorganic refractory oxide matrix or binder. The term "nonzeolitic" asused herein refers to molecular sieves whose frameworks are not formedof substantially only silica and alumina tetrahedra. The term "zeolitic"as used herein refers to molecular sieves whose frameworks are formed ofsubstantially only silica and alumina tetrahedra such as the frameworkpresent in ZSM-5 type zeolites, Y zeolites, and X zeolites. Examples ofnonzeolitic crystalline molecular sieves which may serve as the activealkylation or transalkylation component of the catalyst includesilicoaluminophosphates, metalloaluminophosphates, ferrosilicates,chromosilicates, borosilicates, pillared clays, delaminated clays andcrystalline silicas such as silicalite. Examples of zeolitic crystallinemolecular sieves which may be used as the active alkylation ortransalkylation component of the catalyst include those selected fromthe group of Y zeolites, fluorided Y zeolites, X zeolites, zeolite beta,zeolite L, zeolite omega and modifications of such zeolites. It ispreferred that the molecular sieve used in the catalyst of the inventionhave a Constraint Index below about 1.0 and pores defined by 12-memberedrings of oxygen atoms.

The preferred molecular sieves for use in the catalyst of the inventionare Y zeolites and modified Y zeolites. U.S. Pat. No. 3,130,007, thedisclosure of which is hereby incorporated by reference in its entirety,describes Y-type zeolites having an overall silica-to-alumina mole ratiobetween about 3.0 and about 6.0, with a typical Y zeolite having anoverall silica-to-alumina mole ratio of about 5.0.

The modified Y zeolites suitable for use in preparing the catalyst ofthe invention are generally derived from Y zeolites by treatment whichresults in a significant modification of the Y zeolite frameworkstructure, usually an increase in the framework silica-to-alumina moleratio to a value typically above 6.0. It will be understood, however,that, in converting a Y zeolite starting material to a modified Yzeolite useful in the present invention, the resulting modified Yzeolite may not have exactly the same X-ray powder diffraction patternfor Y zeolites as is disclosed in U.S. Pat. No. 3,130,007. Thed-spacings may be shifted somewhat due to a shrinkage in the unit cellsize caused by an increase in the framework silica-to-alumina moleratio. The essential crystal structure of the Y zeolite will, however,be retained so that the essential X-ray powder diffraction pattern ofthe modified zeolite used in the catalyst will be consistent with thatof either Y zeolite itself or a Y zeolite of reduced unit cell size.Examples of modified Y zeolites that can be used in preparing thecatalyst of the invention include ultrastable Y zeolites,steam-stabilized Y zeolites and dealuminated Y zeolites.

Steam-stabilized Y zeolites are Y zeolites which have beenhydrothermally treated to increase the framework silica-to-alumina moleratio but not the overall silica-to-alumina mole ratio of the zeolite.Steam stabilization normally involves calcination of the ammonium orhydrogen form of the Y zeolite starting material at relatively hightemperatures, typically above about 900° F., in the presence of steam.This treatment results in the expulsion of tetrahedral aluminum fromframework into nonframework positions, but normally does not remove thealuminum from the zeolite and therefore does not increase the overallsilica-to-alumina mole ratio of the starting Y zeolite.

A preferred steam-stabilized Y zeolite for use as the starting molecularsieve in preparing the catalyst of the invention is one produced by (1)ammonium exchanging a Y zeolite to a sodium content between about 0.6and 5 weight percent, calculated as Na₂ O, (2) calcining theammonium-exchanged zeolite at a temperature between about 600° F. and1650° F. in the presence of steam at a water vapor partial pressure ofat least 0.2 p.s.i.a., preferably above about 2.0 p.s.i.a., and mostpreferably between about 5.0 and 15 p.s.i.a., to reduce the unit cellsize of the ammonium-exchanged zeolite to a value in the range betweenabout 24.35 and about 24.65 Angstroms, preferably between about 24.40and 24.64 Angstroms, and then (3) ammonium exchanging the steam-calcinedzeolite to replace at least 25 percent of the residual sodium ions andobtain a zeolite product containing less than about 1.0 weight percentsodium, preferably less than about 0.6 weight percent sodium, and mostpreferably below about 0.2 weight percent sodium, calculated as Na₂ O.Such a Y zeolite is highly stable and maintains a high activity. Thezeolite is described in detail in U.S. Pat. No. 3,929,672, thedisclosure of which is hereby incorporated by reference in its entirety.The same or similar zeolites are now sold by UOP (formerly the LindeDivision of Union Carbide Corporation) as LZY-82 zeolite, by PQCorporation as CP300-56 and by Conteka-BV as CBV-530 and CBV-531. Theammonium exchange steps described above may be facilitated by adding anacid to the ammonium solutions utilized in carrying out the exchanges.

The dealuminated Y zeolites that can be used as the starting molecularsieve for preparing the catalyst are Y zeolites which have beenchemically treated with acids, salts, or chelating agents to increasethe overall silica-to-alumina mole ratio. A preferred group ofdealuminated zeolites is prepared by dealuminating a Y zeolite having anoverall silica-to-alumina mole ratio below about 6.0 and is described indetail in U.S. Pat. Nos. 4,503,023 and 4,711,720, the disclosures ofwhich patents are hereby incorporated by reference in their entireties.A preferred member of this group is known as LZ-210, a zeoliticaluminosilicate molecular sieve available from the Linde Division of theUnion Carbide Corporation. LZ-210 zeolites and other zeolites of thisgroup are conveniently prepared from a Y zeolite starting material inoverall silica-to-alumina mole ratios between about 6.0 and about 20,although higher ratios are possible. Preferred LZ-210 zeolites have anoverall silica-to-alumina mole ratio of about 6.1 to about 16.Typically, the unit cell size is at or below 24.65 Angstroms and willnormally range between about 24.40 and about 24.60 Angstroms. LZ-210zeolites having an overall silica-to-alumina mole ratio below 20generally have a sorptive capacity for water vapor of at least 20 weightpercent based on the anhydrous weight of the zeolite at 25° C. and 4.6millimeters mercury water vapor partial pressure. Normally, the oxygensorptive capacity at 100 millimeters mercury and -183° C. will be atleast 25 weight percent. In general, LZ-210 zeolites are prepared bytreating Y zeolites with an aqueous solution of a fluorosilicate salt,preferably a solution of ammonium hexafluorosilicate.

Before the molecular sieve to be utilized in the catalyst of theinvention is combined with the porous, inorganic refractory oxide whichwill serve as the binder or matrix for the sieve, it will normally becatalytically active for alkylation and transalkylation reactions andcontain ammonium ions. The activity of the molecular sieve is typicallydependent on the amount of alkali metals associated with the acid sitesof the sieve. Some of the molecular sieves that are suitable for use inthe catalyst, such as the steam-stabilized Y zeolite described above,will already contain ammonium ions and have such a low concentration ofsodium or other alkali metal cations that they will possess therequisite activity and can be combined directly with the refractoryoxide component. If, however, the molecular sieve contains a highconcentration of sodium or other alkali metal cations, it is normallydesirable to exchange the sieve with ammonium ions to lower the alkalimetal content and provide the sieve with ammonium ions.

The ammonium ion exchange is carried out by mixing the molecular sievewith an aqueous solution containing a dissolved ammonium salt, such asammonium nitrate, ammonium sulfate, ammonium chloride and the like. Theresulting slurry is stirred for between about 1 and about 5 hours attemperatures above ambient but less than 100° C. If sodium levels below0.50 weight percent are desired, the ion exchange procedure willnormally have to be repeated at least once. Typically, the ion exchangeprocedure will be repeated at least twice and occasionally several timesto reduce the sodium or other alkali metal content preferably to below0.2 weight percent, calculated as Na₂ O.

The molecular sieve possessing alkylation and/or transalkylationactivity is combined with one or more inorganic refractory oxidecomponents, or precursors thereof, such as alumina, silica, titania,magnesia, zirconia, beryllia, a naturally occurring clay, such askaolin, hectorite, sepiolite, attapulgite, montmorillonite orbeidellite, silica-alumina, silica-magnesia, silica-titania, mixturesthereof and other such combinations and the like. Examples of precursorsthat may be used include peptized alumina, alumina gel, hydratedalumina, silica-alumina hydrogel and silica sols. The inorganicrefractory oxide components or precursors thereof, which serve as amatrix for the molecular sieve, are typically amorphous and are usuallymixed or comulled with the molecular sieve in amounts such that thefinal dry catalyst mixture will comprise (1) between about 50 and about95 weight percent molecular sieve, preferably between about 70 and 95weight percent, and (2) between about 5 and 50 weight percent of one ormore inorganic refractory oxides, preferably between about 5 and 30weight percent.

The desired inorganic refractory oxide component(s) or precursor(s)thereof is typically mulled, normally in the form of a powder, with theammonium-exchanged molecular sieve particles. After mulling, the mixtureis extruded through a die having openings of a cross sectional size andshape desired in the final catalyst particles. The catalyst may be madein any shape extrudates including, among others, extrudates having thecross section of a circle or a three-leaf clover similar to the shapeshown in FIGS. 8 and 8A of U.S. Pat. No. 4,028,227, the disclosure ofwhich is hereby incorporated by reference in its entirety. Normally, thelength of the catalyst particles ranges between about 0.10 and 0.50 inchand the diameter between about 0.03 and 0.08 inch. The preferred sizesof the catalyst particles are described in detail in U.S. Pat. No.4,185,040, the disclosure of which is hereby incorporated by referencein its entirety. After the extruded catalyst has been broken intoparticles of the desired length, the catalyst particles are dried andsubjected to calcination at an elevated temperature, normally betweenabout 600° F. and about 1600° F., preferably between about 700° F. andabout 1200° F., to produce a catalyst of high crushing strength.

It has typically been the practice in the art of making molecularsieve-containing catalysts of any type to carry out the finalcalcination step at temperatures that are sufficiently high to not onlyprovide the high crushing strength required of the catalyst but also todecompose substantially all of the ammonium ions in the molecular sieveinto ammonia and hydrogen ions, thereby activating the catalyst byremoving ammonia which the active acid sites in the molecular sieve. Ithas now been surprisingly found that the selectivity of alkylation andtransalkylation catalysts prepared as described above is substantiallydecreased if most or all of the ammonium ions are decomposed duringcalcination. If the catalyst does not contain sufficient ammonium ions,the selectivity of the catalyst for monoalkylation, particularly for thealkylation of benzene with propylene to produce cumene and thetransalkylation of benzene with diisopropylbenzene to produce cumene,will be decreased to such an extent that deleterious amounts ofundesirable by-products will be present in the desired product. It hasbeen found that, for the alkylation catalyst to have optimum selectivityfor the desired monoalkylate, the ammonium ion concentration in thecatalyst must be above about 250 ppmw, calculated as (NH₄)₂ O on avolatiles-free basis.

In view of the above and in accordance with the invention, thecalcination of the extruded catalyst particles is carried under time andtemperature conditions sufficient to leave more than 250 ppmw ammoniumions, calculated as (NH₄)₂ O on a volatiles-free basis, in the catalyst.Typically, the calcination is carried out such that the calcinedcatalyst particles will contain greater than about 1000 ppmw ammoniumions, calculated as (NH₄)₂ O on a volatiles-free basis, preferably morethan about 2000 ppmw, more preferably greater than about 3000 ppmw, andmost preferably greater than about 4000 ppmw. Since ammonia neutralizesacid sites of the active molecular sieve, too high a concentration inthe form of ammonium ions will result in decreasing the activity of thealkylation catalyst. Thus, it is normally not desirable to leave morethan about 20,000 ppmw ammonium ions, calculated as (NH₄)₂ O on avolatiles-free basis, in the catalyst. Although such a relatively highconcentration of ammonium ions will perhaps have a beneficial effect onselectivity, it most likely will have a deleterious effect on catalystactivity. Thus, the ammonium ion concentration of the catalyst must beselected so that there is a balance between selectivity and activity.Typically, the concentration of ammonium ions in the catalyst will rangebetween about 2000 and about 15,000 ppmw ammonium ions, calculated as(NH₄)₂ O on a volatiles-free basis, preferably between about 3000 andabout 10,000 ppmw, and most preferably between about 4000 and about 8000ppmw.

As mentioned previously, the discovery that the ammonium ionconcentration of a molecular sieve-based alkylation or transalkylationcatalyst beneficially affects the selectivity of the catalyst is quitesurprising in light of the conventional practice of decomposingsubstantially all of the ammonium ions during calcination in order toobtain optimum catalytic performance. Although the invention is notlimited to any theory of operation, it is believed that this surprisingphenomenon is due to the fact that alkylation reactions require weakeracid sites than cracking reactions and that undesirable by-productsresult from cracking larger molecules during alkylation. It is thereforebelieved that the selectivity of an alkylation or transalkylationcatalyst is greatly improved by preferentially blocking highly acidicsites in the active molecular sieve component of the catalyst withammonium ions.

Catalysts prepared as described above are useful in a wide variety ofalkylation and transalkylation processes in which an alkylated organiccompound is produced by contacting an organic feedstock with an organicreactant in the presence of the catalyst. Alkylation can be broadlydefined as the addition or insertion of an alkyl group into a molecule.Thus, alkylation reactions are diverse in nature. In transalkylationreactions, which are closely related to alkylation reactions, an alkylgroup moves from one molecule to another. The catalyst of the inventionis effective in catalyzing both alkylation and transalkylation reactionswith consistently high selectivity. In addition, the catalyst of theinvention can be used to catalyze other acid catalyzed chemicalconversion reactions such as isomerization and disproportionationreactions, particularly isomerization and disproportionation reactionsinvolving aromatic and aliphatic compounds.

In general, the catalyst of the invention can be used to catalyze thealkylation of saturated and unsaturated, branched and straight chain,aliphatic compounds, monocyclic and polycyclic aromatic compounds andsubstituted derivatives of such monocyclic and polycyclic compounds, andcycloaliphatic compounds. The alkylating agent used may be any compoundcapable of reacting with the compound to be alkylated. Typicalalkylating agents include alkenes or olefins, alcohols such as methanol,alkylhalides, esters, ethers, aldehydes, ketones, amines, andthiocyanates. The catalyst of the invention can also be used in anytransalkylation process in which a polyalkylated organic compound isconverted into a lesser alkylated or nonalkylated organic compound bytransferring one or more alkyl groups from the polyalkylated compound toa similar compound containing fewer alkyl groups.

Although the catalyst of the invention can be used in anytransalkylation or alkylation process, its preferable uses are inprocesses for the alkylation of aromatic hydrocarbons with C₂ -C₄olefins to produce monoalkyl aromatic compounds and in thetransalkylation of aromatic compounds to produce monoalkyl aromaticcompounds. Normally, the alkylating agent used in such alkylationprocesses will be ethylene, propylene, isobutene or n-butene. Usually amonoalkylated product is desired, but polyalkylated products can also beproduced by, for instance, using toluene as the aromatic compound andethylene as the alkylating agent.

The catalyst of the invention is preferably used in alkylation andtransalkylation reactions to make cumene from benzene and propylene andto make ethylbenzene from benzene and ethylene. Cumene is commonly usedas an intermediate to produce phenol while ethylbenzene is primarilyused as an intermediate in producing styrene. FIG. 1 in the drawingillustrates a specific embodiment of the process of the invention inwhich the catalyst of the invention is utilized both as an alkylationand a transalkylation catalyst. This embodiment of the invention can beused to produce either cumene (isopropylbenzene) or ethylbenzenedepending on whether the alkylating agent utilized is propylene orethylene. When the process is utilized to produce cumene, propylene ispassed through line 10 into line 14 where it is mixed with makeupbenzene introduced into line 14 through line 12 and recycled benzeneintroduced into line 14 through line 16. The source of recycled benzenewill be described in more detail hereinafter. The resultant mixture ofpropylene, makeup benzene and recycled benzene is passed through line 14into preheater 20 and then through line 22 into adiabatic alkylationreactor 24.

The alkylation reactor may contain one or more beds of the catalyst ofthe invention. In the upper portion of the catalyst bed in thealkylation reactor, propylene reacts with benzene to produce cumene andpolyalkylated aromatic compounds such as di- and triisopropylbenzenes.In the lower part of the reactor, these polyalkylated benzenes undergotransalkylation by reacting with benzene to form additional cumene. Thetemperature in preheater 20 is controlled, depending upon the feedcomposition, to yield the desired maximum temperature in the alkylationreactor Typically, the temperature in the alkylation reactor will bebetween about 200° F. and 900° F., preferably between about 300° F. and600° F., and is sufficiently low that ammonium ions in the catalyst arenot decomposed and the formation of xylene is minimized. The pressureutilized in the reactor will range between about 150 p.s.i.g. and 2000p.s.i.g., preferably between about 400 p.s.i.g. and 1500 p.s.i.g. Theweight hourly space velocity typically ranges between about 2 and 2000reciprocal hours, preferably between about 4 and 100 reciprocal hours.The mole ratio of benzene to propylene used typically ranges betweenabout 1.0 and 100, preferably between about 4 and 40. The conditions oftemperature and pressure are preferably correlated so that a liquidphase is present in the reactor. An excess of benzene is utilized inorder to minimize the formation of polymers of the alkylating agent andundesired polyalkylated compounds.

The effluent from reactor 24 will contain, among other compounds,cumene, unreacted benzene, diisopropylbenzene, triisopropylbenzene,n-propylbenzene, ethylbenzene and other aromatic compounds This mixtureis withdrawn from alkylation reactor 24 through line 26, depressured andpassed into line 28 where it is mixed with a recycle stream containingcumene which is introduced into line 28 through line 30. The mixture inline 28 is then passed into condenser 32 where the mixture is cooled todistillation temperature. The cooled mixture is then passed through line34 into distillation column 36 where unreacted benzene is taken overheadvia line 38 and recycled in part to alkylation reactor 24 via lines 16,14 and 22.

The bottoms product from distillation column 36, which comprises cumene,diisopropylbenzene and other benzene-derived impurities, is passedthrough line 40 to distillation column 42 from which the desired productcumene is recovered overhead through line 44. The bottoms product fromcolumn 42 is passed through line 46 into distillation column 48 whereindiisopropylbenzene is removed overhead through line 50 while a bottomsfraction comprising high boiling undesirable by-products is removed fromthe distillation column through line 52 to prevent build up of suchcompounds in the system.

The overhead stream from distillation column 48 is passed through line50, mixed with benzene withdrawn overhead of distillation column 36through lines 38 and 18, and passed through line 54 to preheater 56 andthen through line 58 into transalkylation reactor 60. Here the mixtureof diisopropylbenzene and benzene is passed over the catalyst of theinvention under conditions such that transalkylation occurs, i.e.,propyl groups are equilibrated from the diisopropylbenzene to thebenzene to form additional isopropylbenzene or cumene, which is thedesired product from this embodiment of the invention. Thetransalkylation reactor is normally operated at a temperature betweenabout 250° F. and about 550° F., preferably between about 275° F. toabout 500° F., such that at least some of the reactants are present inthe liquid phase The pressure in the transalkylation reactor willtypically range between about 50 p.s.i.g. and about 2000 p.s.i.g.,preferably between about 100 p.s.i.g. and 700 p.s.i.g. The weight hourlyspace velocity will normally range from about 0.5 to 50 reciprocalhours, preferably between about 1 and 15 reciprocal hours. The moleratio of benzene to diisopropylbenzene introduced into the reactor willgenerally range between about 1 and about 50, preferably between about 5and about 40.

The effluent from transalkylation reactor 60 is withdrawn through line62 and passed through line 30 to line 28 where it is mixed with thebottoms from alkylation reactor 24 and subsequently passed throughdistillation column 36 to distillation column 42 for recovery of theadditional cumene produced in the transalkylation reactor.

Pilot plant tests using different batches of alkylation andtransalkylation catalysts containing a steam-stabilized Y zeolite as theactive alkylation component indicate that the levels of the contaminantethylbenzene in the product cumene that would be recovered overhead ofdistillation column 42 through line 44 in FIG. 1 will vary and that somecatalyst batches will yield levels of ethylbenzene that are unacceptablyhigh, thereby making it necessary to use additional equipment or processmodifications to reduce ethylbenzene concentrations in the productcumene. The use of such additional equipment or process modifications ona commercial scale would be highly expensive. Thus, in an effort toavoid such additional expenditure, the reason for the high amounts ofethylbenzene in the product was sought. It was surprisingly discoveredthat these undesirably high amounts of ethylbenzene are caused by theuse of catalysts which contained low concentrations of ammonium ions,concentrations less than about 250 ppmw, calculated as (NH₄)₂ O on avolatiles-free basis. By providing the catalyst with an ammonium ionconcentration higher than this minimum level, the amount of ethylbenzenecontamination in the product cumene can be reduced to a value such thatno further processing of the product cumene is necessary.

It will be understood that the flow scheme set forth in FIG. 1 can beused to produce ethylbenzene as a desired product by simply substitutingethylene for the propylene introduced into the process through line 10.When this is done, ethylbenzene instead of cumene is recovered overheadof distillation column 42 through line 44 and diethylbenzene andtriethylbenzene are passed through lines 54 and 58 into transalkylationreactor 60 where they are converted via reaction with benzene intoadditional ethylbenzene product.

The nature and objects of the invention are further illustrated by thefollowing example which is provided for illustrative purposes only andnot to limit the invention as defined by the claims. The exampledemonstrates that the production of undesired by-products duringtransalkylation is minimized and therefore selectivity to the desiredproduct is maximized if the catalyst contains greater than a residualamount of ammonium ions.

EXAMPLE

Three catalysts containing different concentrations of ammonium ionswere prepared by mulling mixtures of the steam-stabilized, modified Yzeolite known as LZY-82 zeolite with Catapal alumina that had beenpeptized with nitric acid. The mulled mixtures were extruded through aclover leaf shaped die and dried overnight at 110° C. The driedextrudates were calcined in air under conditions such that theconcentration of ammonium ions in Catalysts 1 and 3 was, respectively,50 and 5800 ppmw, calculated as (NH₄)₂ O on a volatiles-free basis.Catalyst 2 was derived from Catalyst 3 by recalcining Catalyst 3 tolower its ammonium ion concentration from 5800 ppmw to 220 ppmw,calculated as (NH₄)₂ O. Each of the three calcined catalysts contained90 weight percent LZY-82 zeolite and 10 weight percent alumina. Theammonium ion concentration of each catalyst was separately determined byadding a ground sample of each catalyst to a caustic solution anddistilling off as much ammonia as could be generated from each sampleusing a commercial ammonia-by-distillation apparatus (Tecator KjeltecDistillation System Model 1030). The evolved ammonia was trapped in aboric acid solution which was titrated to determine the amount ofammonia evolved from each catalyst sample. The ammonium ionconcentration of each catalyst was then calculated from this number.

The three catalysts prepared as described above were evaluated forselectivity in producing cumene by the transalkylation of benzene withdiisopropylbenzene as described below. Ten grams of each catalyst wereseparately placed in the form of a fixed bed in a pilot plant sizereactor vessel surrounded by a constant temperature fluidized sand bathto control the reactor temperature. A mixture of 91 weight percentreagent grade benzene and 9 weight percent reagent gradediisopropylbenzene isomers, primarily 1,4-diisopropylbenzene, was thenpassed downwardly through the catalyst bed at temperatures rangingbetween 305° F. and 365° F. and at a pressure of 500 p.s.i.g. The weighthourly space velocity was 2.4 reciprocal hours. The reactor temperaturewas varied between 305° F. and 365° F. to control conversion of thediisopropylbenzene. The liquid effluent from the reactor was collectedfor 12 hour periods and then analyzed by gas chromotography using aflame ionization detector. Typical concentration ranges of some of thecompounds found in the reactor effluent over a wide range of conversionsis set forth below in Table 1.

                  TABLE 1                                                         ______________________________________                                        Typical Product Yields                                                                         Typical Yield Ranges                                         Compound         (Mole Percent)                                               ______________________________________                                        cumene           6.0-8.0                                                      benzene          90-92                                                        1,3 diisopropylbenzene                                                                         0.4-0.9                                                      1,2 diisopropylbenzene                                                                         0.002-0.006                                                  1,4 diisopropylbenzene                                                                         0.2-0.6                                                      1,2,4 triisopropylbenzene                                                                      0.003-0.001                                                  n-propylbenzene  0.00-0.01                                                    ethylbenzene     0.00-0.02                                                    1,1 diphenylpropane                                                                            0.005-0.010                                                  ______________________________________                                    

As can be seen from Table 1, the yield of ethylbenzene is quite lowcompared to the desired cumene. However, the product cumene obtained viathe process depicted in FIG. 1 may contain concentrations ofethylbenzene which may require, at substantial capital investment,additional equipment or process modifications to produce cumene at thedesired purity level. Because of this, it is normally desirable that theyield of ethylbenzene in both the alkylation and transalkylationreactors be kept to a minimum. Thus, the performance of Catalysts 1through 3 was evaluated by plotting in FIG. 2 the ethylbenzeneconcentration in the effluent from the above-described transalkylationreactor versus the diisopropylbenzene conversion. Each data point wasobtained by averaging the measured compositions and calculatedconversions over a several day period of steady state operation. Thedata in FIG. 2 indicate that low concentrations of ammonium ions in thecatalyst tend to yield undesirably high concentrations of ethylbenzene,i.e., concentrations over 0.002 mole percent, even at diisopropylbenzeneconversions below 80 percent where commercial operations normally takeplace.

To more clearly show the effect of ammonium ion concentration in thecatalyst on selectivity, the data in FIG. 2 was replotted in FIG. 3 toshow how the ethylbenzene concentration varied with changes in theammonium ion concentration of the catalyst at diisopropylbenzeneconversion levels of 55, 65 and 75 percent. These conversion levels aretypical for commercial operations. As can be seen from FIG. 3,undesirably large amounts of ethylbenzene are obtained with catalystswhich contain ammonium ion concentrations below about 250 ppmw,calculated as (NH₄)₂ O on a volatiles-free basis. The data indicatethat, in order to maintain the concentration of undesirable ethylbenzenebelow 0.002 mole percent at diisopropylbenzene conversions below 75percent, the catalyst should contain concentrations of ammonium ionsgreater than about 2000 ppmw. The data also show that catalystscontaining greater than about 6000 ppmw ammonium ions will decrease theyield of undesirable ethylbenzene to below 0.001 mole percent. Since arelatively high concentration of ammonium ions can deleteriously affectthe activity of an alkylation catalyst, the effects on selectivity shownin FIG. 3 must be balanced against the effects on activity in order todetermine the optimum concentration of ammonium ions. Typically, thisconcentration will range somewhere between 1000 and 18,000 ppmw,calculated as (NH₄)₂ O on a volatiles-free basis, preferably betweenabout 2000 and about 15,000 ppmw, more preferably between about 3000 andabout 10,000 ppmw, and most preferably between about 4000 and 8000 ppmw.

Although this invention has been primarily described in conjunction withan example and by reference to embodiments thereof, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing descriptionAccordingly, it is intended to embrace within the invention all suchalternatives, modifications and variations that fall within the spiritand scope of the appended claims.

We claim:
 1. A catalyst composition comprising a molecular sieve havingalkylation and/or transalkylation activity and an inorganic refractoryoxide component, wherein said catalyst composition contains aftercalcination greater than about 500 ppmw ammonium ions, calculated as(NH₄)₂ O on a volatiles-free basis.
 2. A catalyst composition as definedby claim 1 wherein said catalyst composition is substantially devoid ofhydrogenation metal components.
 3. A catalyst composition as defined byclaim 1 wherein said molecular sieve is a zeolitic molecular sieve.
 4. Acatalyst composition as defined by claim 3 wherein said zeoliticmolecular sieve has a Constraint Index less than about 1.0.
 5. Acatalyst composition as defined by claim 3 wherein said zeoliticmolecular sieve is a Y zeolite.
 6. A catalyst composition as defined byclaim 5 wherein said Y zeolite has a silica-to-alumina mole ratio lessthan about
 20. 7. A catalyst composition as defined by claim 1 whereinsaid molecular sieve is a modified Y zeolite.
 8. A catalyst compositionas defined by claim 7 wherein said modified Y zeolite is asteam-stabilized Y zeolite prepared by the process comprising:(1)ammonium exchanging a sodium Y zeolite to a sodium content between about0.6 and 5 weight percent, calculated as Na₂ O, (2) calcining theammonium-exchanged zeolite at a temperature between about 600° F. and1650° F. in the presence of steam at a water vapor partial pressure ofat least about 0.2 p.s.i.a. to reduce the unit cell size of saidammonium-exchanged zeolite to a value in the range between about 24.35and about 24.65 Angstroms, and (3) ammonium exchanging thesteam-calcined zeolite to reduce the sodium content of the zeolite belowabout 0.6 weight percent, calculated as Na₂ O.
 9. A catalyst compositionas defined by claim 8 wherein said steam-stabilized Y zeolite is LZY-82zeolite.
 10. A catalyst composition as defined by claim 1 wherein saidcatalyst composition contains greater than about 2000 ppmw ammoniumions, calculated as (NH₄)₂ O on a volatiles-free basis.
 11. A catalystcomposition as defined by claim 1 wherein said catalyst compositioncontains greater than about 3000 ppmw ammonium ions, calculated as(NH₄)₂ O on a volatiles-free basis.
 12. A catalyst composition asdefined by claim 1 wherein said catalyst composition contains greaterthan about 4000 ppmw ammonium ions, calculated as (NH₄)₂ O on avolatiles-free basis.
 13. An alkylation catalyst prepared by the processcomprising:(a) extruding a mixture of at least one inorganic refractoryoxide component and a molecular sieve having alkylation and/ortransalkylation activity to form extrudates, wherein said molecularsieve has been ion-exchanged with ammonium ions; and (b) calcining saidextrudates under conditions such that the concentration of ammonium ionsin said extrudates after said calcination is between about 500 and about20,000 ppmw ammonium ions, calculated as (NH₄)₂ O on a volatiles-freebasis.
 14. An alkylation catalyst as defined by claim 13 wherein saidmolecular sieve is a steam-stabilized Y zeolite prepared by the processcomprising:(1) ammonium exchanging a sodium Y zeolite to a sodiumcontent between about 0.6 and about 5 weight percent, calculated as Na₂O; (2) calcining the ammonium-exchanged zeolite at a temperature betweenabout 600° F. and about 1650° F. in the presence of steam at a watervapor partial pressure of at least about 0.2 p.s.i.a. to reduce the unitcell size of said ammonium-exchanged zeolite to a value in the rangebetween about 24.40 and about 24.64 Angstroms; and (3) ammoniumexchanging the steam-calcined zeolite to reduce the sodium content ofthe zeolite below about 0.6 weight percent, calculated as Na₂ O.
 15. Analkylation catalyst as defined by claim 14 wherein said steam-stabilizedY zeolite is LZY-82 zeolite.
 16. An alkylation catalyst as defined byclaim 15 wherein said inorganic refractory oxide component is alumina.17. An alkylation catalyst as defined by claim 14 wherein saidextrudates are calcined under conditions such that the ammonium ionconcentration in said extrudates is between about 1000 and about 18,000ppmw, calculated as (NH₄)₂ O on a volatiles-free basis.
 18. Analkylation catalyst as defined by claim 14 wherein said extrudates arecalcined under conditions such that the ammonium ion concentration insaid extrudates is between about 2000 and about 15,000 ppmw, calculatedas (NH₄)₂ O on a volatiles-free basis.
 19. An alkylation catalyst asdefined by claim 14 wherein said extrudates are calcined underconditions such that the ammonium ion concentration in said extrudatesis between about 3000 and about 10,000 ppmw, calculated as (NH₄)₂ O on avolatiles-free basis.
 20. An alkylation catalyst as defined by claim 14wherein said extrudates are calcined under conditions such that theammonium ion concentration in said extrudates is between about 4000 andabout 8000 ppmw, calculated as (NH₄)₂ O on a volatiles-free basis.
 21. Acatalyst composition as defined by claim 7 wherein said modified Yzeolite is a steam-stabilized Y zeolite.
 22. A catalyst composition asdefined by claim 7 wherein said modified Y zeolite is a dealuminated Yzeolite.
 23. A catalyst composition as defined by claim 7 wherein saidmodified Y zeolite is an ultrastable Y zeolite.
 24. A catalystcomposition as defined by claim 21 wherein said inorganic refractoryoxide component is alumina.
 25. An alkylation catalyst as defined byclaim 13 wherein said molecular sieve is a steam-stabilized Y zeolite.26. An alkylation catalyst as defined by claim 13 wherein said molecularsieve is a dealuminated Y zeolite.
 27. An alkylation catalyst as definedby claim 13 wherein said molecular sieve is an ultrastable Y zeolite.28. A process for making an alkylation catalyst having an ammonium ionconcentration greater than about 500 ppmw ammonium ions, calculated as(NH₄)₂ O on a volatile-free basis, which comprises:(a) extruding amixture of at least one inorganic refractory oxide component and amolecular sieve having alkylation and/or transalkylation activity toform extrudates, wherein said molecular sieve has been ion-exchangedwith ammonium ions; and (b) calcining said extrudates under conditionssuch that the concentration of ammonium ions in said extrudates aftersaid calcination is greater than about 500 ppmw ammonium ions,calculated as (NH₄)₂ O on a volatiles-free basis.
 29. A process asdefined by claim 28 wherein said molecular sieve is a steam-stabilized Yzeolite.
 30. A process as defined by claim 28 wherein said molecularsieve is a ultrastable Y zeolite.
 31. A process as defined claim 28wherein said molecular sieve is a dealuminated Y zeolite.
 32. A processas defined by claim 29 wherein said steam-stabilized Y zeolite is LZY-82zeolite.
 33. A process as defined by claim 29 wherein said inorganicrefractory oxide component is alumina.
 34. A process as defined by claim28 wherein said extrudates are calcined under conditions such that theammonium ion concentrations in said extrudates is greater than about2,000 ppmw ammonium ions, calculated as (NH₄)₂ O on a volatiles-freebasis.
 35. A process as defined by claim 28 wherein said extrudates arecalcined under conditions such that the ammonium ion concentration insaid extrudates is between about 3,000 and about 10,000 ppmw, calculatedas (NH₄)₂ O on a volatiles-free basis.
 36. A catalyst compositioncomprising a stabilized Y zeolite having alkylation and/ortransalkylation activity and an inorganic refractory oxide component,wherein said catalyst composition contains after calcination betweenabout 2,000 and about 10,000 ppmw ammonium ions, calculated as (NH₄)₂ Oon a volatiles-free basis.
 37. A catalyst composition as defined byclaim 36 wherein said inorganic refractory oxide component is alumina.38. A catalyst composition as defined by claim 36 wherein said catalystcomposition contains between about 3,000 and about 8,000 ppmw ammoniumions, calculated as (NH₄)₂ O on a volatiles-free basis.
 39. A catalystcomposition as defined by claim 38 wherein said stabilized Y zeolite isLZY-82 zeolite.
 40. A catalyst composition as defined by claim 38wherein said stabilized Y zeolite is prepared by the processcomprising:(1) ammonium exchanging a sodium Y zeolite to a sodiumcontent between about 0.6 and about 5 weight percent, calculated as Na₂O; (2) calcining the ammonium-exchanged zeolite at a temperature betweenabout 600° F. and about 1650° F. in the presence of steam at a watervapor partial pressure of at least about 0.2 p.s.i.a. to reduce the unitcell size of said ammonium-exchanged zeolite to a value in the rangebetween about 24.40 and about 24.64 Angstroms; and (3) ammoniumexchanging the steam-calcined zeolite to reduce the sodium content ofthe zeolite below about 0.6 weight percent, calculated as Na₂ O.